Endocrine Abstracts

Antithyroid drug (ATD) resistant thyrotoxicosis raises difficult management issues. We describe three recent cases of apparent refractory thyrotoxicosis.

Case 1: A 31 year old woman presented in July 2003 with thyrotoxicosis. Despite treatment with carbimazole (CBZ) 20 milligrams tds, serum free thyroxine (FT4) concentrations remained around 60 picomoles per litre (11-20). In October, CBZ dose was increased to 40 milligrams bd and dexamethasone 2 milligrams tds added. Following a three week admission for supervised drug therapy and monitoring, FT4 was 70.8. She was readmitted on 12/12/03 and treatment changed to propylthiouracil (PTU) 200 milligrams 5 times daily and prednisolone 60 milligrams daily (supervised administration). However, ten days later FT4 was 68.1. She ultimately underwent thyroidectomy in March 2004.

Case 2: A 43 year old woman was diagnosed with Graves' thyrotoxicosis in January 2003. Despite CBZ dose increases to 40 milligrams bd, she remained moderately thyrotoxic and admission was planned. On admission FT4 had fallen to 20.8 and she was therefore discharged the next day, but one month later FT4 had risen to 31.7. PTU 300 milligrams tds was then substituted and prednisolone 30 milligrams od added. Interestingly, this regimen achieved satisfactory control of her thyrotoxicosis.

Case 3: A 31 year old woman was referred in January 2002 (FT4 72). On CBZ 40-60 milligrams daily her thyrotoxicosis settled and from November 2002 to April 2003 she was euthyroid. However, in June 2003 FT4 was 77.2. Despite increasing CBZ to 120 milligrams daily thyrotoxicosis remained uncontrolled (FT4 33-70). In February 2004 PTU 300 milligrams tds was substituted but her FT4 in August was 40.1. She was recently referred for thyroid surgery.

These cases highlight potential problems in thyrotoxicosis management. It is often difficult to exclude poor adherence, but the mechanisms underlying true ATD resistance are unknown.